Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$154.45	8.839%	$168.1018	$168.10	$168.10	$168.10
Purchase #2	$239.95	8.458%	$260.245	$260.25	$260.25	$260.20
Purchase #3	$29.87	10.168%	$32.9072	$32.91	$32.90	$32.90
Purchase #4	$222.62	3.862%	$231.2176	$231.22	$231.20	$231.20
Purchase #5	$37.57	13.229%	$42.5401	$42.54	$42.55	$42.50
Purchase #6	$49.43	12.153%	$55.4372	$55.44	$55.45	$55.40
Purchase #7	$125.71	13.335%	$142.4734	$142.47	$142.45	$142.50
7 purchase totals =	$859.60		$932.9223	$932.93	$932.90	$932.80